(a) Field of the Invention
The present invention relates to a catalyst for a fuel cell, a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same. More particularly, the present invention relates to a cathode catalyst, and a membrane-electrode assembly and a fuel cell system including the same.
(b) Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell, which uses methanol as fuel.
The polymer electrolyte membrane fuel cell has an advantage of a high energy density, but it also has problems in the need to carefully handle hydrogen gas and the requirement of accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
On the contrary, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell due to a slow reaction rate, but it has the advantages of easy handling of fuel, being capable of operating at room temperature due to its low operation temperature, and no need for additional fuel reforming processors.
In the above fuel cells, a stack that generates electricity includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane between them.